Aldous Huxley died while on LSD. That is, while dying, he requested an injection of LSD. Rather than being an urban legend, this event is well-documented in Albert Hofmann's book, LSD: My Problem Child:

Aldous Huxley died on 22 November of the same year, on the same day President Kennedy was assassinated. From Laura Huxley I obtained a copy of her letter to Julian and Juliette Huxley, in which she reported to her brother- and sister-in-law about her husband's last day. The doctors had prepared her for a dramatic end, because the terminal phase of cancer of the throat, from which Aldous Huxley suffered, is usually accompanied by convulsions and choking fits. He died serenely and peacefully, however.

In the morning, when he was already so weak that he could no longer speak, he had written on a sheet of paper: "LSD-try it-intramuscular-100 mmg." Mrs. Huxley understood what was meant by this, and ignoring the misgivings of the attending physician, she gave him, with her own hand, the desired injection-she let him have the moksha medicine.